This invention is concerned with a perforating gun, to be used for piercing hydrocarbon bearing subsurface strata, of the type attached to the end of the drilling string and is lowered to the desired position downhole. More specifically, this invention relates to a mechanism for automatically separating the perforating gun from the drilling string.
After the gun has been fired, if no mechanism exists for releasing it from the drilling string downhole, the drilling string must be completely pulled from the well simply to remove the spent gun. Pulling the string solely for such purpose would be an uneconomical use of time. An automatic release mechanism is therefore a desirable time saver, and forms of such mechanisms are known in the art. For example, U.S. Pat. Nos. 3,966,236 and 4,066,282 disclose automatic release mechanism operated by a fishing tool lowered down through the drilling string on a cable to unlatch the spent gun. Other types of release mechanisms utilize hydraulic pressure to disconnect the gun from the drilling string.
Both of these classes of release mechanisms not only require a discrete step in the operation, and thus an additional expenditure of time, to unlatch the gun, but also require the use of particular tools or machinery, which are of course subject to malfunction. For example, a wireline shifting tool might fail to properly engage the necessary component downhole in the release mechanism, or, once engaged, should said component stick, the cable might pull loose from the tool leaving an obstruction downhole. Or, a hydraulic system might fail to supply sufficient pressure to trigger a release mechanism leaving the perforating gun coupled to the drill string.
One of the most advantageous features of the subject invention is that it operates automatically upon detonation of the perforating gun, and thus eliminates the time taken by additional manipulations and eliminates the risk of the malfunction of other tools. Additionally, the subject invention releases not only the perforating gun but all components necessary to detonate the gun as well, leaving the bore of the drilling string completely unrestricted and eliminating the need for use of a vent assembly.